Abstract: A vertically adjustable, armrest includes a tubular support constructed for attachment to a chair, an armrest assembly telescopingly positioned in the tubular support, and a height adjustment mechanism slidably received in the armrest assembly. The armrest assembly includes a sleeve and a post. The sleeve includes an opening adapted to receive an operative member on one side. The post includes positional detents extending down the length of a first vertical surface. The height adjustment mechanism includes an actuator rod, an operative member, a locking member, and a resilient member. The actuator rod includes an angled ramp, an inclined surface, and a pair of angled surfaces and the locking member includes teeth which selectively mate with the post detents, an inclined surface, and at least one pair of lateral followers.